Engine cough with carb heat

[benyflyguy]

I fly C182. I’ve noticed a few times now when I have the carb heat pulled and am on final and basically have power back to almost nothing I get this little “chug or cough”. Almost like a cylinder miss. First time I noticed it I thought mycarb heat wasn’t pulled out all the way.
Second time thought it was low fuel on one tank. One pulls more then other. But then on the fill I had at least 5 gal on the one side and 15 on the other.
Third time was with my CFI and it just blipped again and he mentioned that the carb temp was pretty high and probably didn’t need carb heat and we pushed it in and it stopped.
Thinking back all of these were on hot humid days when I was on short final with carbs heat on and very low throttle.
I was always taught with Cessna, “pull the carb heat, it’s a Cessna thing”.
So i guess my question is, is carb heat always necessary?? And fu if not then if on checkride of IR rating is simply checking carb temp as a checklist thing and actively voicing and not pulling carb heat going to get me in trouble???
Thoughts?

 

[sarangan]

Your situation could be carb ice, but even more likely is that your mixture is set too rich.
I had the same issue with our 182. Full rich was actually too rich. Applying carb heat richened it even further causing rough idling and coughing. I did some testing and determined that full rich really should be a couple of turns out, so thats what I do now, and I haven't had that problem since. At high density altitudes we always lean for elevation. I think that is a good technique to follow even at low elevations because I am not sure how the full rich setting is actually determined.

 

[Kenny Phillips]

A carb temperature gauge is a good thing; then one can use carb heat when it's really needed, rather than "by rote".

 

[Dan Thomas]

Gee. Another carb heat/carb ice thread. There are a LOT of threads on this subject.

Carb ice can occur in some engines up to 100°F ambient temperature. The carb is a miniature refrigerator and uses the same principles that refrigerators use. Pressure drop, evaporation, the whole thing. It can drop the incoming air temp by as much as 70°F. Carb ice is NOT just a winter phenomenon.

The old 182s had an overly aggressive carb heating system. They get the air too hot, which means its density is too low, which means the mixture richness goes way up. Lean it or use less heat. As the poster above noted, a carb temp gauge can be a handy thing.

 

[MtnMarcus]

Your situation could be carb ice, but even more likely is that your mixture is set too rich.
I had the same issue with our 182. Full rich was actually too rich. Applying carb heat richened it even further causing rough idling and coughing. I did some testing and determined that full rich really should be a couple of turns out, so thats what I do now, and I haven't had that problem since. At high density altitudes we always lean for elevation. I think that is a good technique to follow even at low elevations because I am not sure how the full rich setting is actually determined.

This. I also turn carb heat off on short final

 

[Tantalum]

Lean it or use less heat. As the poster above noted, a carb temp gauge can be a handy thing.

First thing I thought too when I read the post was that it was running too rich. Do we have an official consensus on what's better though? Leaning or only using partial carb heat?

proponents of leaning have told me that partial carb heat will warm the air just enough but then it will freeze further into the venturi at which point carb heat won't do anything, so treat it as all or none

proponents of partial carb heat have told me that leaning aggressively with carb heat will have issues with actual carb icing where you ingest some ice and water or have issues when you turn off carb heat and go to full power in the case of a go-around, etc (assuming when you cram you neglect the red knob)

 

[Stewartb]

To the OP. The engine miss with a warm
engine at low throttle settings with carb heat is pretty normal. My opinion? Why wait til short final at idle power to apply heat? If you have ice you'll kill the engine, which is not a healthy result. Pull carb heat on downwind while you have some power on and some options if the motor coughs. Me? I push heat off when I turn final. Any ice is gone and I'm ready to to full power if I need it. Whatever sequence you settle on? Do it the same way every time. It should be a habit.

Air too hot? Not likely. I have mine piped from
my muffler shroud. It's hot. Carb heat is to melt ice. I don't want to mess around. Does it enrich the mixture? Sure it does. Manage it.

 

[benyflyguy]

Your situation could be carb ice, but even more likely is that your mixture is set too rich.
I had the same issue with our 182. Full rich was actually too rich. Applying carb heat richened it even further causing rough idling and coughing. I did some testing and determined that full rich really should be a couple of turns out, so thats what I do now, and I haven't had that problem since. At high density altitudes we always lean for elevation. I think that is a good technique to follow even at low elevations because I am not sure how the full rich setting is actually determined.

Glad to know I’m not the only one. Our plane is a 1965H so pretty vintage! My mixture is pull out still not vernier. I’m at 1600’ elevation and don’t lean until at altitude. My EGT is on the far side of the plane so I get my self level with autopilot on before I lean over to get a good look at EGT whole pulling back on the mixture slowly. Never thought to lean on the ground but willing to try when I get up on a hot day soon.

 

[benyflyguy]

Gee. Another carb heat/carb ice thread. There are a LOT of threads on this subject.

Carb ice can occur in some engines up to 100°F ambient temperature. The carb is a miniature refrigerator and uses the same principles that refrigerators use. Pressure drop, evaporation, the whole thing. It can drop the incoming air temp by as much as 70°F. Carb ice is NOT just a winter phenomenon.

The old 182s had an overly aggressive carb heating system. They get the air too hot, which means its density is too low, which means the mixture richness goes way up. Lean it or use less heat. As the poster above noted, a carb temp gauge can be a handy thing.

I always think about carb ice on more humid days. I do look at the carb temp gauge and see where temp is at before I pull so I know if icing is a potential problem. I still pull on downwind but when I really drop the power on short final I find myself pushing it back in when I hear that little chug.

 

[James331]

Your situation could be carb ice, but even more likely is that your mixture is set too rich.
I had the same issue with our 182. Full rich was actually too rich. Applying carb heat richened it even further causing rough idling and coughing. I did some testing and determined that full rich really should be a couple of turns out, so thats what I do now, and I haven't had that problem since. At high density altitudes we always lean for elevation. I think that is a good technique to follow even at low elevations because I am not sure how the full rich setting is actually determined.

That.

 

[benyflyguy]

To the OP. The engine miss with a warm
engine at low throttle settings with carb heat is pretty normal. My opinion? Why wait til short final at idle power to apply heat? If you have ice you'll kill the engine, which is not a healthy result. Pull carb heat on downwind while you have some power on and some options if the motor coughs. Me? I push heat off when I turn final. Any ice is gone and I'm ready to to full power if I need it. Whatever sequence you settle on? Do it the same way every time. It should be a habit.

Air too hot? Not likely. I have mine piped from
my muffler shroud. It's hot. Carb heat is to melt ice. I don't want to mess around. Does it enrich the mixture? Sure it does. Manage it.

This is the way I’m thinking. I pull carb heat when beam the tower or number as part of preland checklist I have more power then. At that point rest of downwind and base to turn To final I still have some power. On short final when I pull that power I can easily push carb heat right in. I don’t think I’ll ice up in that short Period of time plus I don’t really chop until I have field essentially made. So if it chugs at that point I’m still in the clear.
In the archer,arrow, Cherokee and even 172 I used to fly never an issue. This 182H seems to be predictable. First couple of times it happened It spooked me... now when I pull that throttle all the way back I find myself pushing in the carb Heat just because I can hear the engine throttle sounds to low.

 

[charlie]

I've flown a hundred or so 182's maybe 500 hours over the last 53 years. They run poorly with the throttle back and carburetor heat on. They do like to make ice! One that I flew a lot had an ice detector light that was supposed to indicate the presence of ice. The light was on more than it was off. It's a Continental thing not a Cessna thing. The induction system and the location of the carburetor are the cause. Lycomings are just about the opposite seldom making ice because the carburetor is bolted to a sump warmed by engine oil. Better to use heat and not need it than not using it and finding out you needed it the hard way. I had a 182 quit cold on takeoff at about 500 feet at night. Carb icing conditions were present and I had never thought carb ice would happen at takeoff power let alone cause the engine to quit. It was certainly one of the scariest moments in my 10,000 plus hours of flying. Charlie Melot

 

[Stewartb]

What's strange to me is that you can take two same year 180s and they're as close to identical as they can be and one will be an ice maker and the other not. My 180 rarely makes ice. I have 180 owner friends who struggle constantly with ice. And Lycomings aren't all that different. I sold my last Cub to a guy who crashed his Cub after the engine hesitated on go-around, which the investigators attributed to ice, and that plane had a history of it. The Cub I sold him doesn't make ice. Same 0-320-B2B, same carb, same airbox. I'm surprised we don't know more about the whats and whys of carb ice.

 

[denverpilot]

Ours is not a wicked ice maker like some but carb heat on ours usually makes it overly rich.

If you can remember to push the mixture up in a go around, leaning it a bit after applying carb heat will smooth it right back out.

Go try it at altitude sometime if you’re nervous about changing habits down low.

The engine isn’t particularly smart. Poor induction, big six cylinder, blubbers like a Harley with straight pipes...

It’ll talk to you and tell you what it wants.

You can diddle with having the carb idle mixture adjusted to be leaner, too. Can cause opposite problems later in cold weather at sea level... won’t want to start, needs a bunch of prime when cold, won’t want to stay running... if your mechanic over-does it.

You get the idea.

There’s a happy medium somewhere on that idle mixture setup but you can spend a lot of time messing around trying to find it, or just lean it a bit when it’s decided it wants to be a big blubbery baby.

Easier to fix too rich than too lean, since we have a big red knob.

 

[benyflyguy]

Ours is not a wicked ice maker like some but carb heat on ours usually makes it overly rich.

If you can remember to push the mixture up in a go around, leaning it a bit after applying carb heat will smooth it right back out.

Go try it at altitude sometime if you’re nervous about changing habits down low.

The engine isn’t particularly smart. Poor induction, big six cylinder, blubbers like a Harley with straight pipes...

It’ll talk to you and tell you what it wants.

You can diddle with having the carb idle mixture adjusted to be leaner, too. Can cause opposite problems later in cold weather at sea level... won’t want to start, needs a bunch of prime when cold, won’t want to stay running... if your mechanic over-does it.

You get the idea.

There’s a happy medium somewhere on that idle mixture setup but you can spend a lot of time messing around trying to find it, or just lean it a bit when it’s decided it wants to be a big blubbery baby.

Easier to fix too rich than too lean, since we have a big red knob.

Thanks. That is something to try out at altitude and see how it works. It’s reassuring to hear I’m not alone. Going to read and learn more about my carb temp gauge. If anything I’m more aware of what’s going on carb wise. I think trying a slight lean might do the job. I’ve got about 50 hours in this plane so far and I think I’m just starting to get to know her, a little...

 

[Jeff Oslick]

Another experienced 182 pilot here to tell you to use your carb temp gauge, religiously. I don't think I've ever used carb heat descending to the runway. I *do* use carb heat very soon after takeoff fairly often, to keep the carb temps in the low to mid 40s. I've had ice twice at about 400 AGL on departure in our plane (and once even lower climbing out in a O-320 powered PA-28-160).

Your mixture is likely set a bit too rich as well.

 

[Stewartb]

So you run partial heat? Power robber. Mine is all on or all off. For years I've heard guys say partial carb heat evens out their temps. I never found any benefit in doing it but my temps are very even.

 

[Jeff Oslick]

So you run partial heat? Power robber. Mine is all on or all off. For years I've heard guys say partial carb heat evens out their temps. I never found any benefit in doing it but my temps are very even.

Yes, we do run partial quite often. Yes, it evens out our temps too. We are in a constant battle with our induction system to get reasonably even temps. Beyond that, what is the point of running full carb heat if you only need partial heat to prevent ice?

 

[Stewartb]

If it works for you? Go for it. It doesn’t work for me in my plane. I can run all day with carb temps below freezing and not make ice. I ran my 180 with a carb temp instrument that had a yellow range on it for close to 15 years. The instrument said to avoid operation in the yellow range, which would have required partial carb heat about 100% of the time. I never used carb heat and never had a carb ice problem. That instrument went into the trash when I re-did my panel.

 

[Dan Thomas]

If it works for you? Go for it. It doesn’t work for me in my plane. I can run all day with carb temps below freezing and not make ice. I ran my 180 with a carb temp instrument that had a yellow range on it for close to 15 years. The instrument said to avoid operation in the yellow range, which would have required partial carb heat about 100% of the time. I never used carb heat and never had a carb ice problem. That instrument went into the trash when I re-did my panel.

If it didn't make ice when the carb body was below freezing, the air was too dry. Any ice that forms is almost instantly stripped away by the dry airflow, just like frost doesn't form on a flying wing even when the airplanes on the ground are frosting up.

 

[Stewartb]

Sublimation. My favorite way to defrost wings in winter.

My 180 is not an ice maker. A guy I know who has the same model and the same PPonk motor has nightmares with making ice in the same locations on the same day. It’s a head scratcher.

 

[flyingbrit]

I've always wondered if there's a mistake in that diagram. Most forms of icing are worst, i.e. have the greatest temp and dew point range at 100% RH as one would expect. Except for pressure carburetors, which are worst at 80% RH and apparently immune at 100% RH. Can anyone explain this?